Biochemical characterization of the cholecystokinin receptor on CHP212 human neuroblastoma cells

Cholecystokinin (CCK) receptors reside on a large number of cell types along the digestive tract and in the nervous system. A human neuroblastoma cell line (CHP212) has recently been described to express a type A receptor, with structural specificity similar to that on pancreatic acinar cells and gall bladder smooth muscle cells but different from the predominant type of binding site found in brain (type B). In this work, we have performed photoaffinity labeling and protease peptide mapping of the CHP212 receptor and have compared it to other type A CCK receptors. ¹²⁵I-D-Tyr-Gly-[(Nle^28,31,pNO₂-Phe³³)-CCK-26-33], a probe that possesses a photolabile residue at position 33 within the theoretical receptor-binding domain of this hormone, specifically labeled a M(r) = 80,000-90,000 glycoprotein on this cell line, while labeling larger proteins (M(r) = 85,000-95,000) on rat pancreas and human gall bladder. Deglycosylation with endo-β-N-acetylglucosaminidase yielded bands of M(r) = 43,000 from CHP212 and gall bladder and M(r) = 42,000 from pancreas. Peptide mapping of the deglycosylated bands using Staphylococcus aureus V8 protease demonstrated identical patterns in CHP212 and gall bladder and a similar but different pattern in pancreas. Thus, although possessing heterogeneity in their carbohydrate domains, CCK receptors on human neuroblastoma cells (CHP212) and human gall bladder smooth muscle cells have highly similar or identical protein cores. The core protein on another type A CCK receptor, from rat pancreas, appears to differ from these, likely representing molecular heterogeneity between species.